As is well known, a fuel cell is a system for generating electric energy through an electrochemical reaction between oxygen and hydrogen contained in hydrocarbon materials such as methanol, ethanol, and natural gas.
Recently developed polymer electrolyte membrane fuel cells (hereinafter, referred to as PEMFCs) exhibit excellent output characteristics, low operating temperatures, and fast starting and response characteristics. Therefore, the PEMFCs have a wide range of application including as mobile power sources for vehicles, as distributed power sources for homes or buildings, and as small-sized power sources for electronic apparatuses.
A fuel cell system employing the PEMFC scheme basically includes a stack, a reformer, a fuel tank, and a fuel pump. The fuel pump supplies fuel stored in the fuel tank to the reformer which reforms the fuel to generate hydrogen. The hydrogen and an oxygen supply such as air are fed to the stack which constitutes an electricity generator set having a plurality of unit cells.
In such a conventional fuel cell system, the reformer generates hydrogen from the hydrogen-containing fuel through a catalytic chemical reaction using thermal energy. Accordingly, the reformer generally includes a heat source for generating the thermal energy, a reforming reactor for absorbing the thermal energy and generating hydrogen gas from the fuel, and one or more carbon-monoxide reducing reactors for reducing the concentration of carbon monoxide in the hydrogen gas.
In such a conventional reformer, since the reforming reactor and the carbon-monoxide reducing reactors are separate from one another, the heat source should be separately provided to supply different ranges of thermal energy to the reforming reactor and the carbon-monoxide reducing reactor, respectively.
Therefore, since the structure of the reformer is complex, it is difficult to make the entire fuel cell system compact. In addition, since the heat exchange between the reaction parts is carried out through pipes, its heat delivery properties are inefficient.